Synthesis And Modification Of Spherical Sulfur Cathode Materials For Lithium-Sulfur Batteries

Due to the high theoretical capacity of1675mAh/g, high theoretical energy density of2600Wh/kg, the advantage of abundant source and environmental friendliness, lithium-sulfur batteries have attracted the attention of researchers before30years ago. However, some problems hinder the commercial application of lithium-sulfur batteries such as the complex mechanism of lithium-sulfur batteries, easy to shuttle and low conductivity. The conventional lithium-ion battery can not meet the demand of the commercial development because the highest theoretical capacity is only300mAh/g and lower capacity can be obtained in application. Hence, recent research has focused on the development of lithium-sulfur batteries again. It is found that to construct nano/micro-materials for the cathode of lithium-sulfur batteries is an efficient method to improve the lithium-sulfur batteries. In this paper, we develop novel spherical sulfur materials and decorate them by using metals to improve the electrochemical performanceIn chapter3, the micro-sphere sulfur was synthesized by the co-precipitation method using sodium polysulfide as sulfur source. Compared with sublimed sulfur, the micro-sphere structure can obviously improve the sulfur’s performance in the discharge/charge process due to the smaller size and unique morphology, In addition, other three kinds of sulfur particles were synthesized by adding different agent to change the construction and morphology of the sulfur. Compared with others, the micro-sphere sulfur synthesized by adding F127showed the highest capacity of1050mAh/g at0.02C and630mAh/g at0.1C.In chapter4, the surface modification and decoration of micro-sphere sulfur were further performed to coat a porous metallic structure using chemical reduction, which were used to improve the electrochemical property. The characterization of SEM, TEM, EDX and the electrochemical tests of CV, EIS and galvanostatic charge and discharge indicated that the modification of sulfur with metal (Pt, Ni, etc) coatings can improve the electrochemical stability and the charge/discharge performance with a high current rate.